1. Field of the Invention
The present invention relates to a fluid compressor with a vertical longitudinal axis for use. e.g. in a refrigerating apparatus, the fluid compressor sucking a low-pressure refrigerant gas and discharging a high-pressure compressed gas.
2. Description of the Related Art
The inventor of the present invention proposed a fluid compressor, e.g. in Japanese Patent Application No. 2-228000.
In this proposed apparatus, a cylinder and a piston are eccentrically arranged within a sealed casing, and the piston is provided with a helical groove having a pitch decreasing from one end towards the other end. A similarly helical blade is fitted in this groove so that the blade can project from and retreat in the groove.
The space between the piston and the cylinder is divided into a plurality of working chambers.
A rotor is situated around the cylinder, and an annular stator is fixed on the inner wall of the sealed casing with a small gap between itself and the outer periphery of the rotor. The rotor and the stator constitute a motor.
Power is supplied to the motor so that the rotor and cylinder can rotate as one unit. The torque of the cylinder is transmitted to the piston via a torque transmission mechanism. Thus, the cylinder and piston rotate synchronously at a relative circumferential speed, with the positional relationship therebetween maintained.
In accordance with the rotation, the blade projects from and retreats in the groove in the radial direction of the piston.
A refrigerant gas in a refrigerating cycle is sucked in the cylinder, conveyed from the suction-side working chamber to the discharge-side working chamber. While the gas is conveyed, it is gradually compressed.
The refrigerant gas pressurized up to a predetermined level is once discharged to the internal space of the sealed casing and then returned to the outside of the compressor via an exhaust pipe connected to the sealed casing.
In the above type of fluid compressors, the longitudinal axes of rotational parts such as a piston and a cylinder are, in general, situated horizontally. However, in some types of refrigerating apparatuses, the axes of such rotational parts are situated vertically, because of the limited space occupied by other structural parts.
In the compressors having rotational parts with vertical longitudinal axes, the rotational parts tend to descend due to their own weights.
When the rotational parts are stopped, the lower end face of the piston abuts on a lower bearing for supporting the piston, but this abutment state remains unchanged at the time of rotation.
Specifically, the piston comprises a piston body and upper and lower shaft portions integrally formed at the upper and lower ends of the piston body. At the time of rotation, too, the upper surface of the lower bearing functions as a thrust surface and it comes in sliding contact with the lower end face of the piston body.
Accordingly, a very considerable friction loss occurs between the bearing and the piston. Consequently, an increase in electric input is incurred. In the case of a motor with controllable rotation speed, the input increases in accordance with the increase in rotation speed, resulting in a disadvantage in operation costs. Moreover, noise occurs and quiet operation cannot be performed.